Decoder and method for performing decoding operation using map algorithm in mobile communication system

Abstract

A turbo decoder and a decoding method are disclosed, which use a Maximum A Posteriori (MAP) algorithm in order to perform iterative decoding. The method has the steps of sequentially receiving input data in a memory having a predetermined window size and performing a forward metric calculation for the input data so that the input data has a four window size, performing a first backward metric calculation for the input data and outputting first valid data when the data are input to the memory by twice the window size, and performing a second backward metric calculation for the input data and outputting second valid data when the data are input to the memory by three times the window size.

1. A method for performing iterative decoding by a decoder in a mobile communication system using a turbo code, the method comprising the steps of:
 a) performing, via a decoding device, a forward metric calculation for sequentially input data by means of one memory corresponding in size to four times a window of predetermined size; 
 b) performing, via a decoding device, a first backward metric calculation for the input data when the forward metric calculation is performed for the input data by a size of three times the window in said one memory; and 
 c) performing, via a decoding device, a second backward metric calculation for the input data when the forward metric calculation is performed for the input data by four times the window size in said one memory. 
 
     
     
       2. The method in  claim 1 , further comprising a step of performing a forward metric calculation or a backward metric calculation through said one memory. 
     
     
       3. The method in  claim 1 , wherein step a) further comprises a step of performing a forward alpha metric calculation for the input data so that the input data has a four window size and performing iterative decoding. 
     
     
       4. The method in  claim 1 , wherein step b) further comprises a step of performing a first backward beta metric calculation for data corresponding in size to two windows, outputting valid data, and performing iterative decoding, when the forward metric calculation is performed for the input data of three times the window size. 
     
     
       5. The method in  claim 1 , wherein step c) further comprises a step of performing a second backward beta metric calculation for data of three times the window size, outputting valid data, and performing iterative decoding, when the forward metric calculation is performed for the input data having four times the window size. 
     
     
       6. The method in  claim 1 , further comprises a step d) of selectively outputting a first backward beta metric calculation value and a second backward beta metric calculation value, comparing the first backward beta metric calculation value and the second backward beta metric calculation value with an alpha metric calculation value, and controlling iterative decoding. 
     
     
       7. A decoding apparatus for performing iterative decoding in a mobile communication system using a turbo code, the decoding apparatus comprising:
 one memory for outputting input data having four times a window of predetermined size in the forward direction or a backward direction; 
 an alpha metric block for performing a forward metric calculation for sequentially inputting data so that the data has a size of four times the window; 
 a first metric block for performing a first backward metric calculation for the input data, when a forward calculation is performed for the input data having a size of three times the window; and 
 a second metric block for performing a second backward metric calculation for the input data, when a forward calculation is performed for the input data having four times the size of the window. 
 
     
     
       8. The decoding apparatus in  claim 7 , wherein said one memory is a memory for performing a forward metric calculation or a backward metric calculation. 
     
     
       9. The decoding apparatus in  claim 7 , wherein the metric block is a block for performing a forward alpha metric calculation for the input data so that the input data have a size of four times the window, and for performing iterative decoding. 
     
     
       10. The decoding apparatus in  claim 7 , wherein the first metric block is a block for performing a first backward beta metric calculation for data of two window sizes, outputting valid data, and performing iterative decoding, when the forward metric calculation is performed for the input data having a size of three times the window size. 
     
     
       11. The decoding apparatus in  claim 7 , wherein the second metric block is a block for performing a second backward beta metric calculation for data having a size three times the window size, outputting valid data, and performing iterative decoding, when the forward metric calculation is performed for the input data having a size that is four times the window size. 
     
     
       12. The decoding apparatus in  claim 7 , further comprising a beta buffer for alternatively storing valid data of the first metric block and valid data of the second metric block. 
     
     
       13. The decoding apparatus in  claim 7 , further comprising a Log-Likelihood Ratio (LLR) block for comparing the calculation value of the alpha metric block, valid data of the first metric block, and valid data of the second metric block with one another, and controlling iterative decoding.